Confused with 0TA3080

[Tom Adam]

Can't check the whole discussion here, but when in doubt, check the 
datasheet of the OTA and built the test schematic. I did this once for 
+/-500 CA3280's I bought for cheap. Turned out +/-30% was broken. Later 
I sold a lot of them and I made a lot of profit out of it.

And I think CGS has a WASP pcb for 15AUS$, I would buy this one and 
compare with yours.

Cheers,
ToAd
Op 20-1-2013 22:17, Tony Hardie-Bick schreef:
> On 20/01/13 21:04, Marc Nostromo [M-.-n] wrote:
>>> if you remove R7, the voltage at pins 2 and 3 of the first ota 
>>> whould be
>>> half the supply voltage. if you put R7 beck in circuit, the dc level
>>> shouldn't change much.
>>
>> So, If I have R10,R9 connected, I get half voltage. i.e. 2.5v
>>
>> However as soon as I connect them to the ota, the voltage goes to 3.6.
>> Pin 2 doesn't really matter. Pin 3 makes the voltage change (R7 is
>> disconnected).
>
> pin 3 is a diode to ground (base-emitter junction of an npn input 
> transistor in
> the internal curcuit from the CA3080 datasheet), so connecting R10.R9 
> to pin 3
> should, if anything, reduce the voltage, but you are seeing an increase.
>
> i'm not there in person, and can see i'm tired from mistakes i've made
> earlier, but this does look suspicious
>
> Tony (HB)
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